Bed angle sensor for reducing ventilator-associated pneumonia

ABSTRACT

Apparatus for indicating the angular position of a patient support surface such as a mattress relative to the direction of gravity is disclosed. An angle sensor mounted to a frame associates with the patient support surface to create an output responsive to changes in position relative to gravity. Circuitry transmits an output signal to activate a display of the angular position of the patient support, thereby indicating whether the angular position is within a predetermined range. Preferably, the apparatus has a circuit for activating an indicator light, which more preferably mounted above the patient support surface. In certain preferred embodiments the apparatus that comprises the light is connected to the headboard, or the like. It is preferred that the apparatus has a memory device for storing positional information comprising at least a predetermined angular measurement, and more specifically that there is a device for storing information pertaining to the length of time said patient support has been set to an angular position is within a predetermined range.

The present invention relates to medical devices for patient care andmonitoring and more specifically relates to methods and apparatus forhospital beds and the like.

BACKGROUND OF THE INVENTION

Critically ill patients on mechanical ventilation in the Intensive CareUnit (ICU) are at high risk for developing a variety of nosocomial(hospital-acquired) infections. The most common of these infections isventilator-associated pneumonia, which complicates the course of almost30% of patients undergoing mechanical ventilation. Patients withventilator-associated pneumonia have a mortality rate that approaches50%. Ventilator-associated pneumonia also results in a prolongedduration of mechanical ventilation, increased length of ICU stay andhigher healthcare costs.

The pathogenesis of ventilator-associated pneumonia is generallyrecognized to consist of two steps: 1) bacterial colonization of thestomach and oropharynx, and 2) subsequent pulmonary aspiration ofcontaminated secretions. Mechanically ventilated patients are prone togastric bacterial colonization due to the widespread use of histamine-2(H2) receptor blockers and proton pump inhibitors for the prevention ofgastrointestinal stress ulceration. Indwelling nasogastric andnasoenteric feeding tubes decrease the competence of the loweresophageal sphincter, increasing the potential for aspiration.Strategies to reduce the incidence of ventilator-associated pneumoniaare typically aimed at reducing the colonization of the aerodigestivetract, decreasing the incidence of aspiration, or both. Becausegastroesophageal aspiration is facilitated by supine body position, itis recommended that the head of a patient's bed be elevated to about30-45 degrees at all times, as clinically tolerated, to reduceaspiration of contaminated secretions and subsequent development ofventilator-associated pneumonia.

Thus, maintenance of the head of the bed at about 30-45 degrees is aclinically useful method for reducing a patient's risk ofventilator-associated pneumonia and ICU mortality. These concepts arewell developed in the literature, see for example, Kollef et al., “Theprevention of ventilator-associated pneumonia.” NEJM 1999; 340:627-634;Dodek et al., “Evidence-based clinical practice guideline for theprevention of ventilator-associated pneumonia.” Ann Intern Med 2004;141:305-313. Based on these and numerous other studies, the Centers forDisease Control and Prevention recommends that patients receivingmechanical ventilation have the head of the bed elevated between about30 degrees and 45 degrees to prevent nosocomial pneumonia. However, useof higher backrest positions for critically ill patients is not a commonnursing practice. Backrest elevation may be affected by the accuracy ofnurses' estimates of patients' positions. Current recommended practiceis summarized in: “Getting Started Kit: Prevent Ventilator-AssociatedPneumonia” a copy of which is available at the website:http://www.ihi.org/NR/rdonlyres/A448DDB1-E2A4-4D13-8F02-16417EC52990/0/VAPHowtoGuideFINAL.pdf

Despite evidence of the effectiveness of this simple intervention,mechanically ventilated ICU patients are commonly not maintained at ahead-of-bed angle that decreases their risk for the development ofventilator-associated pneumonia. See “Effect of Standardized Orders andProvider Education on Head-of-Bed Positioning in Mechanically VentilatedPatients.” Helman et al. Crit Care Med 31(9):2285-2290, 2003. Inrecognition of this fact, a device was recently developed that providesa simple indicator mounted to the side of a bed that uses a weighthanging from a thread to visually confirm whether the head of the bed iselevated at precisely 30 degrees. See Chest Physician, February 2006, p.8. The disclosed device requires a clear view and adequate lighting andmust be visually checked on a regular basis.

Numerous systems for controlling and providing data regarding theposition of a patient relative to the vertical (or horizontal) areknown. These systems are often complicated electromechanical devicesthat use feedback from pressure sensors and similar devices to adjustboth the position of the bed as well as the contours and firmness of thebed surface (usually an air or fluidized bead mattress). For example,U.S. Pat. No. 6,353,950—Bartlett, et al. discloses a positional feedbacksystem for a medical mattress. The apparatus adjusts the pressures of atherapeutic mattress surface in accordance with the angular position ofthat surface and has both an angular position sensor and a rotationsensor.

There remains, however, a long-felt and as of yet unmet need for adevice that is both simple and robust that can verify that the angle ofa patient's bed is within a certain criterion. Prior art devices areeither overly complex and related to highly sophisticated bed systems,or are inadequate as monitoring devices particularly if the beds withwhich they are used are moved or are surrounded by other equipment, indimly lit areas or other wise difficult to access from the side for aninspection of the angle. It would therefore be desirable to provide asystem that has a visual indication of bed angle and that can be viewedin a variety of settings, e.g., while the patient is in a ward, in anICU unit, in transit, in an elevator, etc. It would be further desirableto provide a device that is inexpensive and that can be part of a newlymanufactured bed, or retrofitted into existing beds.

SUMMARY OF THE INVENTION

Accordingly, it has now been found that the shortcomings of the priorart can be overcome by providing an apparatus for indicating the angularposition of a patient support surface such as a mattress relative to thedirection of gravity by mounting an an angle sensor to a frameassociated with the patient support surface and having an outputresponsive to changes in the angle sensor's position relative togravity, in which the angle sensor has circuitry for transmitting anoutput signal to activate a display of the angular position of thepatient support to indicate whether the angular position is within apredetermined range. In certain embodiments, the angle sensor comprisesan enclosure to house said angle sensor and an inclinometer having anoutput that correlates position to the direction of gravity. Preferably,the apparatus has a circuit for activating an indicator light, whichmore preferably is connected to the enclosure and mounted above thepatient support surface. In certain preferred embodiments the apparatuscomprises a headboard (or footboard) and the light is connected to theheadboard (or footboard), but in certain embodiments the indicator lightis remote from the enclosure, and may optionally use a wirelesstransmitter for transmitting a signal to activate the light. It ispreferred that the apparatus has a memory device for storing positionalinformation comprising at least a predetermined angular measurement, andmore specifically that there is a device for storing informationpertaining to the length of time said patient support has been set to anangular position is within a predetermined range.

Methods of indicating the angular position of a patient support surfacerelative to the direction of gravity are also disclosed. In accordancewith the present invention an angle sensor is mounted to a frameassociated with the patient support surface and an output responsive tochanges in said angle sensor's position relative to gravity force iscreated. An output signal to activate a display of the angular positionof said patient support is then transmitted and the display indicateswhether the angular position is within a predetermined range, preferablyby turning a light on or off.

The present invention also relates to methods of determining the angularposition of a patient support surface relative to the direction ofgravity, comprising: the steps by observing a display of the angularposition of said patient support to indicate whether the angularposition is within a predetermined range. Preferably, the step ofobserving a display comprises observing a light mounted either to aframe associated with the patent support surface or mounted to a remotelight display and whether the light is turned on or turned off.Additionally, in certain preferred embodiments, the step of observing adisplay also comprises observing an indication of a time period duringwhich the patent support surface has been positioned within apredetermined range, again preferably by observing whether a light isturned on or turned off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a typical hospital bed illustrating apreferred embodiment of the present invention;

FIG. 2 is a side elevation view of the bed illustrated in FIG. 1 showingthe head of the bed elevated;

FIG. 3 is a side elevation view of another preferred embodiment of thepresent invention;

FIG. 4 is a schematic of a circuit used in preferred embodiments of thepresent invention; and

FIGS. 5A-5B are, respectively, a side elevation view of anotherpreferred embodiment of the present invention and a remote indicationsystem used in conjunction with this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown a typical hospital bed 10 thatincludes a frame that supports a patient support surface. In someinstances, the patient support surface will be a mattress and in othersit will be integrated with the frame. The present invention is usefulwith beds, but is similarly useful with other devices that supportpatients such as operation and examination tables, gurneys, carts andthe like as well as transport structures built into transportationvehicles and the like.

Still referring to FIG. 1, in accordance with the present invention, acentral unit 100 is mounted to the frame of the bed 10. As shown, thecentral unit 100 is mounted underneath the head of the bed, however, thecentral unit 100 can be mounted to the side of the frame and asexplained below can be mounted in other locations and is preferablysecured in place with either Velcro strips or clamps. It is possiblethat in some applications the bed will be frameless or have internalsupport structures and thus the central unit will be affixed to thepatient support surface itself. The central unit 100 preferably is madeof radiolucent material and has a battery clip door to allow access forbattery changes (in those embodiments that include a battery). Theembodiment illustrated in FIG. 1 represents a preferred embodiment formaintaining a patient elevated at an angle such that the incidence ofventilator associated pneumonia is reduced. Referring now to FIGS. 1-2it can be seen that the head of the bed is elevated and when elevated,an indicator light 110 is activated (or alternatively can bedeactivated). In certain embodiments the indicator light will beactivated only when the elevation angle is within a predetermined limit,either a narrow limit such as 29.5-30.5 degrees, or a broader limit suchas 30-45 degrees. In other embodiments the indicator light will glow onecolor if the head of the bed is elevated to the correct angle and willglow another color when the angle is incorrect. Other indicator signalssuch as flashing lights or sound effects can also be included to alertpersonnel that the incorrect bed angle has been set. The presentinvention provides an advantageous monitoring system that is not undulycomplex and is easily checked visually, yet because the indicator light110 is mounted in a visible area, the side of the bed itself need not beinspected. The indicator light 110 can be mounted to either a footboardor headboard associated with the bed or may be remote from the bed, inthe same room or in another room, on a wall above the bed or connectedvia a wired or wireless connection to any conceivable location and toany of a number of display devices included but not limited to dedicatedmonitoring panels, computer or other existing monitor screens or remotemonitor screens or similar devices such as PDAs.

Referring now to FIG. 3 an alternate embodiment of the present inventionis illustrated. The bed 10 is the same as shown in FIGS. 1-2; however,in this instance the central unit 100 is mounted in the central regionof the bed and monitors the elevation angle of the thighs. As will beunderstood by those skilled in the art, in addition to ventilatorassociated pneumonia, there are myriad medical conditions that aretreated by elevating a patient's limbs or trunk to a certain angle, andrelevant to the embodiment illustrated in FIG. 3, it may be important toelevate the legs to reduce pressure, alter blood flow or reduce theincidence of ulcers, among other things.

FIG. 4 is a schematic of a circuit used in certain preferred embodimentsof the present invention. Generally, this circuit or parts of it will becontained within the central unit 100 illustrated in FIGS. 1-3.Preferably, the circuit will have a power supply, which can be either astorage cell (battery) or power generated by a power supply that iseither part of the device or power taken from another power supplyalready existing on or in the bed or similar structure, typically DCcurrent converted from an AC source. It is preferred that the powersupply be as small as possible and have as long a life as possible.Preferably but not necessarily, the power supply is connected to a powerdisplay (which indicates the presence of power) and to the tilt sensor.The tilt sensor (or inclinometer) preferably includes a memory orequivalent electronic or electromechanical feature that allows apredetermined angle or angular range to be “set.” Additionally, incertain embodiments, the memory will determine and record the time spentat a certain angle, e.g., the time spent with the head of the bedelevated at the specified angle. Tilt sensors and their implementationin hospital beds are well known in the art. One useful type of sensor isdiscussed inhttp://sensors-transducers.globalspec.com/LearnMore/Sensors_Transducers_Detectors/Tilt_Sensing/Tilt_Inclinometers.An example of tilt switches that are commercially available at a varietyof angles is disclosed athttp://www.allproducts.com/ee/jinzonco/32-tilt_switches.html.

As discussed in further detail below, in certain embodiments, theindicator light 110 includes an LED or similar light that is easilyvisible from outside the room and can be mounted or attached to the bedand/or the ventilator. This is connected to the transmitter, via anoutput jack or by other means. As also discussed below, in certainembodiments wireless transmission to a remote light display is alsoincluded. In such wireless embodiments, a bedside monitor or centralnursing station monitor is provided that indicates the status of the bedas being within or outside of the designated angle, (and data relatingto the time set at that angle, if collected and/or if this feature isactivated). The remote light display is attached to the central unit 100by either a wire connected to the output jack, or via wirelesstransmission.

Referring now to FIG. 5A-5B, a wireless embodiment of the apparatus ofthe present invention is illustrated. In general the system illustratedis similar to that shown in FIGS. 1-2 and includes a central unit 100,which further includes a wireless transmitter 210, although as describedabove, a hard-wired connection may be included and a jack or otherconnector would replace the remote transmitter 210. As seen in FIG. 5B,a remote light display 220 would include a wireless receiver 212 (orhard-wired connection) that received a signal from the central unit 100.Indicator lights 214,216 provide information, such as whether the bed iselevated to the chosen angle and if the recommended time duration hasbeen achieved.

Although certain embodiments of the present invention have beendescribed with particularity, these embodiments are illustrative and donot limit the present invention. In particular, the present invention isnot limited to a particular bed, gurney, cart or other patient handlingdevice, nor is it limited to the specific conditions and anglesillustrated and described. These embodiments are provided to enable oneof skill in the art to make and use the invention. Upon review of theforegoing, numerous adaptations, modifications, and alterations willoccur to those skilled in the art. These will all be, however, withinthe spirit of the present invention. Accordingly, reference should bemade to the appended claims in order to ascertain the true scope of thepresent invention.

1. An apparatus for indicating the angular position of a patient supportsurface relative to the direction of gravity, comprising: an anglesensor mounted to a frame associated with the patient support surfaceand having an output responsive to changes in said angle sensor'sposition relative to the direction of gravity, said angle sensorcomprising circuitry for transmitting an output signal to activate adisplay of the angular position of said patient support surface, thecircuitry comprising a circuit for activating an indicator light toindicate whether the angular position is within a predetermined range,wherein said indicator light comprises a base, an upwardly extendingpost and a light affixed to a distal end of said post, wherein the baseis disposed upon a surface remote from the angle sensor, whereby thelight is visible from a position remote from the patient support surfacewhile looking in the direction of the patient support surface.
 2. Theapparatus according to claim 1, wherein said angle sensor comprises: anenclosure to house said angle sensor; and an inclinometer having anoutput that correlates position to the direction of gravity.
 3. Theapparatus according to claim 1, wherein the display is removablyattached to the surface.
 4. The apparatus according to claim 1 whereinsaid indicator light is connected to the enclosure and mounted above thepatient support surface at a point remote from the enclosure so as to bevisible from a remote location while looking in the direction of thepatient support surface.
 5. The apparatus according to claim 4 whereinthe apparatus comprises a headboard or footboard, and the indicatorlight is disposed upon one of the ventilator, headboard or footboard. 6.The apparatus according to claim 1 wherein said indicator light is alight display remote from the enclosure.
 7. The apparatus according toclaim 6 wherein the circuit comprises a wireless transmitter fortransmitting a signal to activate the light.
 8. The apparatus accordingto claim 1 further comprising a memory device for storing positionalinformation comprising at least a predetermined angular measurement. 9.The apparatus of claim 8 wherein the memory device further comprises adevice for storing information pertaining to the length of time saidpatient support has been set to an angular position that is within apredetermined range.
 10. The apparatus of claim 1 wherein the anglesensor is mounted to a portion of the bed frame that facilitatesmeasurement of a pertinent angular position.
 11. A method of determiningthe angular position of a patient support surface relative to thedirection of gravity, comprising: the steps of: providing an indicatorlight activated by an angle sensor mounted to a frame associated withthe patient support surface, said indicator light being disposed on apost elevated above upon one of: a ventilator, a headboard or afootboard associated with the patient support surface; and observingsaid indicator light from a position remote from said patient support bylooking at said patient support whether the angular position is within apredetermined range.
 12. (canceled)
 13. The method of claim 11, whereinthe step of observing a display comprises observing whether a light isdisplaying a first color or a second color.
 14. The method of claim 11,wherein the step of observing a display comprises observing whether alight is turned on or turned off.
 15. The method of claim 11, whereinthe step of observing a display comprises observing an indication of atime period during which the patient support surface has been positionedwithin a predetermined range.
 16. The method of claim 15, wherein thestep of observing an indication of a time period comprises observingwhether a light is turned on or turned off.
 17. An method of indicatingthe angular position of a patient support surface relative to thedirection of gravity, comprising: mounting an angle sensor to a frameassociated with the patient support surface; creating an outputresponsive to changes in said angle sensor's position relative togravity force; transmitting an output signal to activate a display ofthe angular position of said patient support, wherein said displaycomprises a base, a post and a light disposed upon said post, whereinsaid display is placed upon a structure associated with the patientsupport surface and remote from the angle sensor; and indicating on thedisplay whether the angular position is within a predetermined range.18. The method of claim 17, wherein the step of indicating on thedisplay whether the angular position is within a predetermined rangecomprises turning a light on or off.
 19. The method of claim 18 furthercomprising the step of mounting the light to one of a footboard or aheadboard associated with the patient support surface.
 20. The method ofclaim 18 further comprising the step of mounting the light at a remotelocation associated with the patient support surface.
 21. The method ofclaim 17 further comprising the step of storing information pertainingto the length of time said patient support has been set to an angularposition that is within the predetermined range.